#include <mpi.h> 
#include <stdio.h>
int main(int argc, char *argv[]){  
	int commsize, my_rank;
	int msg = 0;

	MPI_Init(&argc,&argv);  
	MPI_Comm_size(MPI_COMM_WORLD, &commsize);
	MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
	
	if (my_rank == 0) {
		printf("[%d] msg = %d\n", my_rank, msg);
		if (commsize == 1)
			goto finalize;
		MPI_Send(&msg, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
		MPI_Recv(&msg, 1, MPI_INT, commsize - 1, 0, MPI_COMM_WORLD, NULL);
		printf("[%d] msg = %d\n", my_rank, ++msg);
	}
	else {
		MPI_Recv(&msg, 1, MPI_INT, my_rank - 1, 0, MPI_COMM_WORLD, NULL);	
		printf("[%d] msg = %d\n", my_rank, ++msg);
		if (my_rank + 1 < commsize)
			MPI_Send(&msg, 1, MPI_INT, my_rank + 1, 0, MPI_COMM_WORLD);
		else
			MPI_Send(&msg, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
	}
	
finalize:
	MPI_Finalize();
}